A retrospective study was undertaken in 113 patients with surgically proven pituitary adenomas to correlate the frequency, type, and location of computed tomographic (CT) abnormalities with surgical findings. There were 63 prolactin-secreting, 19 growth-hormone-secreting, 12 adrenocorticotropic-hormone-secreting, two thyroid-stimulating-hormone-secreting, and 17 nonfunctioning adenomas. The 51 functioning and nonfunctioning macroadenomas had similar CT appearances. Only 34 secretory adenomas presented as discrete, focal, hypodense lesions; the rest were isodense with the adjacent pituitary gland. Secretory adenomas were clinically apparent earlier, and accordingly the abnormalities seen on CT were less developed. The location of the normal pituitary gland could not be determined by attenuation characteristics; only by infundibulum displacement or opposite to a discrete, focal, hypodense lesion could the gland location be predicted reliably. Adenomas with hemorrhage, infarction, and cyst formation were indistinguishable from those without these findings. CT was helpful in identifying the mass effect of macroadenomas; however, in microadenomas of all types CT abnormalities were uncommon. Thus, the diagnostic evaluation of the patient suspected of harboring a pituitary adenoma, particularly a microadenoma, must remain a joint effort based on clinical, radiographic, and endocrinologic data.